Differential transmission



Aug. 3, 1965 o. MUELLER 3,198,035

DIFFERENTIAL TRANSMISSION F'iled Aug. 16, 1965 4 Sheetzs-SheefI 1 f2 mfg-T76 3 MMU/7 Fm INVENTOR. 07'7'0 M/E E? @MLM/WWW Aug. 3, 1965 o. MUELLER 3,198,035

DIFFERENTIAL TRANSMISSION Filed Aug. 16, 1963 4 Sheets-Sheet 5 78 7@ 50 INVENTOR.

077'0 M/ELL 5 @MM/WMM O O 55 55 55 58 5556 l 54 @fu @y E U @y pm 5 o m 55 Aug- 3, 1965 o. MUELLER 3,198,035

DIFFERENTIAL TRANSMI SS ION Filed Aug. 16, 1965 4 Sheets-Sheet 4 o J7@ Oi 56 57 5 5e n @a @o f V INVENTOR. 07' TO M/ELE/Q United States Patent O 98,035 DIFFERENTIAL TRANSMISSION Otto Mueller, 13 Byfield Lane, Dearborn, Mich. Filed Aug. 16, 1963, Ser. No. 302,545 13 Claims. (Cl. 74-650) The .present invention relates to a transmission adapted primarily, but not exclusively, for use with motor vehicles. The presen-t invention may be used as a lockingtype differential transmissi-on for a two wheel drive or two of such transmissions may be used to provide a four wheel drive. This invention relates to the invention of prior U.S. application, Ser. No. 284,646, filed May 3l, 1963.

The differential transmissions now in use in the automobile industry employ a set of differential gears in a casing to allow differential action between the driven wheels of the vehicles. This use of differential gears occurs essentially in all makes of automobiles irrespective of whether conventional differential transmissions are lused or whether some form of a locking-type differential transmission is employed.

As is well known, the conventional differential transmission heretofore used in the automobile industry has an inherent defect in that the driving torque is transmit-ted under certain circumstances wholly to the wheel of the vehicle which has the least traction. This loss of power to the other wheel occurs, for example, when the lwheel with less traction is on ice, in mud, or the like where it can spin freely. Considerable efforts have been made for ya number of years in the automobile industry to develop an improved differential transmission which can overcome this defect and which will provide controlled torque to both driven wheels while still assuring tha-t proper differential action between the driven wheels will occur when required, but such efforts have not been entirely successful.

The differential transmission disclosed in the aforesaid prior application, Ser. No. 284,646, overcomes many off .the shortcomings of the prior art, particularly when used in a motor vehicle having a two wheel drive. The differential transmission illustrated in that application can be fused for four wheel drive vehicles, but when so used one unit must be provided -for the rear axle, a second unit must be provided for the front axle and a third differential unit must be provided for the drive shaft assembly operatively connecting the front and rear axle assemblies. The need for the differential unit for the front axle is the :same as that for the rear axle, namely, to allow for differential action between the driven wheels of the axle assembly. The need for the third differential unit in the drive shaft assembly is not so obvious, but it is found that such a uni-t is required if means are not otherwise present to accommodate for greater or lesser turning of the front wheels relative to the rear wheels, or in other words, means must be provided to prevent winding of the drive shaft assembly between the front and rear axles. If no such means are provided, it is found that such winding will occur and will be released periodically with a snap when the torque resulting -fr-o-m such winding action overcomes the frictional resistance on the ground of the `front or rear wheels, causing the f-ront or rear sets of wheels to Spin a limited amount relative to the other.

This problem of compensating Ifor the winding of the ydrive shaft assembly is inherent in all differential transare always in a direct -gear drive with the drive shaft and no .slippage can occur in such direct gear drive. Thus,

ice

when in a four wheel drive, differential gearing is used in conjunction with the front and rear axles, a direct drive between these axles is provided, and a third means -must be provided to compensate for such differential action that may `occur between the front and rear axle assemblies.

It is an object of the present invention to provide 'an improved differential transmission which is constructed :and arranged so that it can be used in the front axle assembly `of .a four wheel drive vehicle and which will function to eliminate the need for a separate differential uni-t between the front and rear axle assemblies.

It is another object of the present invention to provide an improved differential transmission of the foregoing character which can be used in both the -front and rear axle assemblies of a four wheel drive vehicle, eliminating the need for .a separate differential unit between the front and rear axle shaft assemblies, and which can also be used :as the differential transmission in a two wheel drive vehicle.

-It is still another object of the present invention to provide an limproved differential transmission of the foregoing character which employs a hydraulic mechanism for controlling and distributing torque to each of the driven wheels associated with the transmission and which is adapted to use the fluid from the differential case for this purpose :and to replenish itself when required because 0f loss of huid through leakage, or the like.

lIt is another object of the present invention to provide an improved differential transmission of .the roregoing character which lis constructed and arranged so that the hydraulic mechanism is -operably disposed between the differential casing and each of two `different rotary elements, and the t-ransmission .is characterized by the effective and simple manner in which the mechanism is assembled as a part of the transmission.

It is still another object of the present invention t0 .provide a hydraulically actuated differential transmission lwhich is constructed and arranged so that it is statically and dynamically balanced and has various components constructed so that a relatively long and trouble-free life of the transmission is assured.

It is still another object of the present invention to provide an improved differential of the foregoing character in which the hydraulic mechanism is constructed and arranged to allow limited turning of the differenti-al casing relative :to the two driven shafts of the axle assembly when such two driven shafts are turning as a single unit, the rate of such relative turning being controlled by interchangeable flow control means in the hydraulic circuit of the hydraulic mechanism.

It is still another object of the present invention to provide an improved differential transmission of the foregoing character wherein interchangeable flow control members are provided in the hydraulic mechanism for controlling the torque distribution to the driven wheels.

It is still another object of the present invention to provide an improved differential transmission which is constructed and arranged so that its external dimensions will conform generally to those of the prior conventional differential transmissions, including the differential transmission disclosed in aforesaid application, Ser. No. 284,646, making the present differential transmission readily interchangeable with said prior transmissions or making parts of the present transmission interchangeable with corresponding parts of the transmission disclosed in the aforesaid application, Ser. No. 284,646.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Jz-z of FIGURE -1;

y In the drawings: j

FIGURE l is a sectional view taken on line 1 1 of FIGURE 2 of a transmission embodying thepresent in-y vention; E

` 'FIGURE `2 -is a fragmentary'section taken on the line FIGURE 3 is a fragmentary -3-3 of FIGURE 1; E. FIGURE4 is a'fragmentary front elevation with a major portion in section taken on the line 4--4 Vof FIG- URE,2,: Q y, Y.

FIGURE 5 is a `fragmentary section of on the line 5--5 of FIGURE 2; Y

kFIGURE 6iis-a fragmentary section of the casing taken :on the'line 6-6 of FIGURE 2;

FIGUREJ7 is a1 developed viewiof the fluid passages and l Y FIGURE 8 is `an enlarged plan view of the pistons in i the Vhydraulicfmechanism asseen in the direction of thev arrows 8-8 in FIGURE L1. f.

Before explaining the present invention in detail, itjis ment of parts illustrated in the accompanying drawings, since the invention'is capable of other'embodiments and lof beingpracticed or carried out in tvariousrways. Also,

section taken on the line f the casing taken j for the hydraulic mechanism vof the presentv invention;

'to be understood that the invention is not -limited in itsY 'applicatiori to the detailsf of construction' andv arrange-IY it isto be understood thatthel phraseology or terminology employed herein is for the purpose of description and not of limitation., Y V l Referringto the drawings, the illustratedY embodiment ofthe invention will be described vin greater detail. The differential transmissional has a casingn 12 which supports in the conventional manner a ringugear 14'which is adapted to be driven by a drive pinion 16. The cas- 'ing 12 has hollow stems18 and 20 which are mounted in bearings22 and 24. As shown in-FIGURE l, the hollow stem 18 is separable from the remainder of casing 12 for the purpose of assembling internal parts ofthe transmission 10. 'f Bolts (not shown) hold these parts `12 and 18 together. v f

The bearing 24 is mounted in a cap 26 which is adapted A,

to be mounted and held stationary in a conventional differential housing (not shown). Similarly, the outer race "of the bearing 22 is adapted to be held stationaryin Vthe differential housing (not shown). i

Thel casingl 12 has a radiallyy outer portion 28 and 4a radially inner portion which are secured together at thek same time'V that the ring gear 14 is secured to the casing flange32v by the plurality of bolts 34. Asshown-in FIG- 'URE 1,.the,ange 32 has an annular groove 36 for receiving-one end of the radially outer portion 28, and the latter Y has a radially outwardly projecting shoulder 38 against Awhich the ring gear 14 lits to hold the radially outer portion 28 in `place on the radially inner portion 30,v A plurality of O-rings 40 are provided between the various parts de-p ,scribed above to assure that the jointsbetween these parts are sealed for purposesY to rbe described.V

Extending into the oppositeu ends of the casing 12 are axle shafts 42 and 44 which areV externally vsplined on their innerv vendsy in the conventional manner. A 'conven- Vtional spacerf element 146 is provided therebetween.

Mounted-within thecasing 12 for. rotation relative tothe Kcasing 12 about its axis are two :axially aligned rotatable `elements'48 and 50which are' hollow and arci-,internally splined for 'receiving the externally splined end'sgrrespectively, ofaxle shafts 42 and 44.' Thus, rotatable'element 48 and 'axley shaft 42V turn as a unitv and' rotatable elemen 50 and axle 'shaft 44 turn'asanother unit. Y

Rotatable element 48 has formed around a portion of Vits periphery threeradiallyroutwardlydirectedrise and Vfall cam'surfaces 52 (FIGURE f3), and similarly, rotatable element 50also hasaround a portion rof its .pe-

riphery three similar rise and fall cam surfaces 54 (FIG URE 2).y

. Vpreviously described.

v axleassemblies.

assembled in their illustrated (FIGURE 1) Ypositionsby insertion through the end of casing 12 zoccupied by the separable'. hollow stem 18. Y

.- Positioned in each of the pressure chambers 56 are pistons 64 and in the pressure chambers 57 are similar pistons65. The pistons 64, 65 have formed in their inner ends'transverse notches 66in which are seated the folflowers or'r'ollers k68.` The lattery are adaptedl to follow 'or roll von the rise and fall cam surfaces 52 for eie'cting reciprocal movementsof the pistons 64,= 65 in the pres- Y sure chambers 56, 57; lAs shown in FIGURE 4, thepressure chambers are elliptical in cross Vsection and the minor axis ofeach ellipse extends parallel to theaxis of the casing 12. The pistons ,64,` v65 are .also elliptical in shape, as shown in FIGURE 8, and the notches 66 are arranged in pistons 64, 65 sorthattheaxis of each 'follower'or'roller 68 is also parallel to the vaxis .of ,cas-

ing 12.Y By virtue ofthe'se constructions and arrange ments, the followers Vor rollers 68 will r'oll smoothly' on A@the cam surfaces l521and noV problem will arise from the pistons 64, 65turning onltheir individual axes..

The'pistons 64, 65.are constructed also so asto maintain a seal between themselves and the walls of the pressure chambers 56,57. rIn .the illustrated embodiment of the invention the pistons 64, 65 are made from a suitable plastic material and a groove 70`is located in the top wall 'thereof so as to provide la generally outwardly flared lip 72. When the pistons 64, 65 move outwardly in the pressure chambers'56, 57 the lips 72 are designed to maintain the desired sealfor a purpose to be described.

A detailed description of pressure chambers 58, 59 and their Yassociated pistons 74, is not believed necessary because thesegparts are essentially thel'samei'as corre spondingpressure chambers 58,; 59f`and pistons 64, 65,

From the foregoing description it can be understood that when an input torque is imparted to the casing 12 'byrneans of the drive pinion 16 and the ring gear 14, the pressure chambers 56,V 57v and 58,. 59, which are an integral part of casing 12, will travel'therewith. n This has the eiect of moving the followers 68-on the respective cam surfaces` 52 and 54-of rotatable elements A48 and S0.

By controlling the rate of reciprocation of pistons-64, 65 and 74, 75 thatfcan occur, the portion of the input torque to the casing 12 can be distributed in'controlled Vamounts to the rotatable elements `48a1`1d 50and thereby tothe axle shafts 42 and 44. Also, `because this oonstruce tion and arrangement permitsa controlled amount ofV slip- E page to occur "simultaneously betweenI the casing 12 and Vbothrotatable elements48 and 50, it is possible to use Vthe present inventionA as the differential for the front axle assembly of afourrwheel dvevehicle andj thev slippage Vwillfaccommodate any winding-upv that may occur inthe drive assembly interconnecting the frontr and rear wheel The,V construction and arra'ugement'for controlling the 'rate of reciprocation ofthe pistons 64, 65 and 74, l75 will now be explained.YV Formed between Ythel radially! inner and A'outer portions 28 and 30 are three annular vgrooves 76, '78 kand 80. These grooves and .their relationshipto one anotherzand to the pressurechambersS, 57 and 58, 59

can be seen'in the developed illustration in FIGURE 7.

fAs `there shown,v annular'groove `76 communicates via Vducts 82vwith pressure chambers '57 ofthe group of pressure chambers 56, 57 and via ducts 84 with pressure chambers 59 of the group of pressure chambers 58, 59. The second annular groove communicates via ducts 86 with pressure chambers 56, and the third annular groove 80 communicates via ducts 88 with pressure chambers 58. For the purpose of describing the construction and operation of this portion of the invention, the group of pressure chambers 56, 57 and their associated parts for transmitting torque from casing 12 to axle shaft 42 will be described first. For this purpose attention is directed primarily to FIGURES l, 3, and 8. As shown particularly in FIGURE 5, the annular grooves 76 and 78 are ,in controlled fluid communication at the passage means 90 and 92. Access to both of these passage means can be gained by removal of the plugs 94 and 96 located in the end of the radially inner portion of casing 12.

Passage means includes the passageway 998 extending between grooves 76 and 78 and in which is located a fiuid flow control member in through which is a restricted orifice 102. A spring actuated check valve element 104 `is urged into the ow orifice 102 by the compression rspring 106. By virtue of this arrangement fluid can flow from annular groove 78 to annular groove 76 but not in a reverse direction.

Passage means 92 operates in the reverse manner to allow one way flow of uid from annular groove 76 to annular groove 78. Passage means 92 includes a passageway 108 extending between grooves 76 and 78 and in which is located a fluid ow control member 110 through which is a restricted orifice 112. A spring actuated check valve element 114 is urged into the fiow orifice 112 by compression spring 116.

Thus, when the pressure chambers 56, 57 and the annular grooves 76 and 78 as well as the ducts 82 and 86 and the passageways 98 and 108 are full of hydraulic fiuid, a closed hydraulic system is provided and the rate at which the pistons 64, 65 can reciprocate is governed by lthe rate at which the hydraulic fluid can reciprocate back and forth through the flow control orifices 102 and 112. n The construction and operation of the hydraulic mechanism operatively connecting the casing 12 with the axle .shaft 44 is similar to that which has just been described relative to shaft 42. With particular attention to FIG- URE 6, it can be seen that the pressure chambers 58 are vconnected to the pressure chambers 59v by two passage `means118 and 120. Access to passage means 118 and 120 can be gained by removal of the plugs 121. Passage means 118 has a passageway 122, a fluid flow control mem- 4ber 124 with a restricted orifice 126, check valve element to reciprocate by relative turning between the casing 12 `and the rotatable element 50 and its associated axle shaft k44.

From the foregoing description .it can be understood that the rotatable elements 48 and 50 and their associated hydraulic mechanisms connecting them to casing 12 operate substantially independently of one another, and both hydraulic mechanisms are designed to allow simultaneously a small amount of turning of the casing 12 relative to both rotatable elements 48 and 50 and their associated axle yshafts 42 and 44.

It is recognized that events may ioccur, such as leakage orthe like, to cause a partial loss of fluid from the pressure chambers to the casing 12 or the differential housing (not shown). To prevent such leakage O-rings have been kused to minimize this problem. Also, pump means 142 (FIGURE 4) have been provided to compensate for any such leakage that may occur and to assure that the hydraulic system of the differential 10 is always kept full.

Referring to FIGURES 1 and 4, this feature of the invention will be described. As there shown, the stationary cap 26 has an annular cam groove 144 in which is adapted to travel a ball 146 which is located in the bore 148. Urged against ball 146 by compression spring 150 is a reciprocating pump element 152. The Alatter has at its opposite end a hollow cavity 153 in which isk carried a valve element 154 urged into pump inlet 156 by the compression spring 158. The pump inlet 156 is in direct communication with the groove 160 on the external side of casing 12 so that it will always be partially filled, at least, with hydraulic fluid or lubricating oil from the housing (not shown) for the differential 10. Thus, when the pump element 152 is moved to the right (as seen in FIG- URE 4), by action of spring 150 and travel of ball 146 on cam groove 144, hydraulic fluid will be drawn into v the reduced left end portion of bore 148 and on the return stroke (to the left) such fiuid will be trapped in the reduced end of bore 148 because spring 158 will return valve element to its position over pump inlet 156. At this point in the stroke to the left, if there is a shortage of hydraulic fluid in groove 76, the pressure differential between groove 76 and the cavity 153 will cause the compresesd fluid to urge ball check element 162 from its seat and such fiuid will flow via enlarged port 164 and passageway 166 to groove 76.

If the groove 76 and the spaces with which it is in communication are full of hydraulic fiuid, such fluid will prevent ball check element 162 from opening, and on the stroke to the left of pump element 152 the fluid trapped in cavity 153 and the reduced end of bore 148 will flow through duct 168 and annular groove 170 to the by-pass valve 172 for directing the fluid to the internal parts of the differential 10 for lubricating the same. For this purpose, the fluid ows past the spring urged check valve element 174 through the ducts 176, 178 and 180.

Thus, whenever casing 12 is rotating relative to the differential housing (not shown) there will be a pumping action occurring which will replenish any fluid lost from the hydraulic systems described, and continuous forced lubrication of the internal parts of the differential 10 will occur.

As can be readily understood, the described differential 10 will function to allow differential action between the axle shafts 42 and 44 when the rate of relative turning between the axle shafts 42 and 44 does not exceed the rate of allowed turning of rotatable elements V48 and 50. The rate of allowed turning is controlled by the rate at which the pistons 64, 65 and 74, 75 can pump fiuid through the control orifices 102, 112 and 126, 136.

It can be seen that the described differential can be made small in size so as to occupy the space occupied by conventional differentials, and it also utilizes two groups of hydraulic pistons and related structures which are similar to those employed in the differential gear type differential transmission shown in aforesaid application, Ser. No. 284,646 and some of the parts of the present differential can be made interchangeable with corresponding parts -of the aforesaid gear type differential transmission for convenience and low cost of production when a four wheel drive vehicle is built employing the present differential for the front axle assembly and the gear type differential of the aforesaid application for the rear axle assembly.

Having thus described my invention, I claim:

1. A transmission ycomprising a rotatable casing for transmitting an input torque, a pair of coaxially aligned rotatable elements mounted in said casing and adapted to be connected respectively to a pair of shafts, each of said elements having a plurality of circumferentially arranged and radially outwardly directed rise and fall cam surfaces, said casing having means defining in axially spaced relation two groups of circumferentially aligned and radially inwardly directed pressure chambers, one of of the otherof said elements, the pressure chambers of said two groups each being intwo sets, restrictive passage means associated with each groupzproviding fluid corn kmunicationrin each groupbetween the .two'sets of pressure chambers thereof, pistons in said two groups of pressure chambers operatively engaging the cam surfaces that are faced by their respective, groups ofvpressurech'ambers for reciprocation inresponse to' rotationof their vassociated elements relative to saidcasing, saidntwol groups of'pres sure chambers and 4their'associated camesurfaces being f arrangedso that when relative'rotation occurs between said casing and eitherof said elements lthe 'p istonsasso-` ciated with Ithe ca m.l surfaces of such'element reciprocate to transfer the fluidvinthe Yassociated groupmof 'pressure chambers, back and yforth rbetweenits two rsets via `the surfaces, said 4casing having means defining vin ,axially spaced relation two groups of circumferentially aligned and radially -inwardly directed pressure chambers, one of Y said groups facing .the cam surfacesof one of `said elements and the other of said groupsffacing `the cani surfaces of the other of said elements, the pressure chambers of said two groups each beingin two sets, restrictive passage means associated with each group providing fluid communicationincach group between the two sets Vof pressurevchambers thereof, pistons in said two groups of pressure chambers operatively engaging the cam surfaces,

thatY are faced by their respective groups of Ypressure chambers for reciprocation in response to rotation of their associated elements relative to said casing, said two groups of pressure chambers and their associated cam surfaces being arranged to that-when relative rotataion occurs between said casing and either of said elements the pistons associatedwith the cam surfaces of such-element reciprocateto transfer the uid in theassociated group of pressure chambers'back andfforth betweenits two setsvia lthe associated passage means, reciprocating `pump means mounted in said casing in communication with said pas sage means for replenishing losses of uid that may have occurred from said pressure chambers Aor said passage means, and pump actuating means for'eiecting reciprocation of said `pump means including a cam follower eX- tending through one end of said casing and adapted to reciprocate and an annular cam mounted adjacent to 'said one end of said casing andadapte'd to be held stationary relative tol said casing.'v 3. A transmission comprising .a rotatable casing for transmittingan input torque, a pair ,of coaxially aligned be connected respectively to,v a pair of shafts, each of said inwardly directed pressure chambers,A one ofsaid groups facing the cam surfaces of one of said elements and the, other of said groups facing the cam surfaces of the other of said elements, the Ipressure 'chambers o'fY said two groups each beingin two sets, vrestrictive passage means associated with eachrgroupproviding fluid rcommunication -in each groupl between the two sets of pressure chambers thereof, pistons in said two groups of pressure chambers operatively engaging the cam surfaces that are facedv by their vrespective groups ofpressure chambers for reciprocation' in response to rotation of their assolciated elementsrelative to said casing, said two groups Vofpressure chambers and their 'associated cam surfaces rotatable elements mounted in said casing-and adapted to being arranged softhat when/ relative rotation occurs between .said casing, andi eitherjofsaid elementsV the pistons associated with thecamsurfaces' of 'sujchelemen-t reciprof cate to-.transferthe iluidin the-associated Vgroup of 1 pressure'chambe'rs `'back and forth betweenitsitwo" Sets .via theassociated passage means, and flow control means removably mounted in the'portions of saidl passage means associated witheach groupfor, ,selectively setting ,'thelrate of -owj of huid [through suc, f'portionsy of saidA passage means in ',accordance with@ the 'relative turning `ofsaid casing with .respect"tesa-id'V ments.'7 d 4'. A transmission 'comp' gg'ag rotatable casing for transmitting an! input torquela pair, ofcoaxially aligned rotatable elementsin said casing, one of said rotatable elements and said casingbeing :operatively connected by fluid pressure kmeans for -tr'a'nsrriission of' torque, -sa'id one elementV andsaid casing having radially jfacing circumferential' portions, -one .of said portionsjincludinga rplurality of "radially openingfpressuregchambersifacing the otherA porti-on and'adapted to contain duid, the other of said portions including'fradjially directed'rise and V fall cam surfaces,v pistons in'said 'pressure 'chambers operatively engaging saidl cam .surfaces lfor rreciprocation l in response to 4rotation of said oneelementrelative to said casing, said v'pressure vchambers,and Asaidjcam surfaces being arranged so that certain `of, said pist-ons',reciprocate out of phase Awithaotherluf said pt stcnus during relative rotation of said'one elementrelativeto said ,casing,gan d 'passage means `providing restrictedfluid communication between Y,the pressure chambers containing said certainpistons and the pressurevchambers Containing VSaid ,other Pistonsand the other 'fof saidirotatable, `elementsrandA said casing being similarly operatively connected Iby uid pressure means fortransmissicn of to-rgue. l y l, 5. A trans-mission as -claimedin claim 4wherein said cam surfaces are arranged relative to said pressure chambers so thaty relative 4turning of saidA one element relative 'to said casinglwilleifect reciprocationof said certain 'pistons fone-,hundred 'eighty ldegrees 011i 0f Phase 'with Said other pistons.; j. f y

6. A transmission V,as claimed. in claim14jincluding pump meansginl communication with said pressure chambers Vand, responsive to rotation of said transmissionrfor `urgingiluid ,from Van external sourcefto said .pressure chambers for replenishing rlosses'of fluid that may have occurred'from -said pressure chambers or Vsaid passage 7. A transmission' as claimed incl-aim Y6y includes bypass means in Vcommun-icationwith `Vsaid. pump ymeans and havingaV discharge Aoutletin communication with the interior of said casing so that lipid' passing through said 'by-pass means can ,lubricate said rotatable elements and their associated parts. d

AV8. AV transmission comprisinga rotatable casing for 4transmitting an input torque,a pairI of'coaxially' aligned rotatable ,elements in said casingnoneof'said rotatable Aelements and saidcasingjbeing operatively 'connected Iby fluidfpressure; meansfor ktransmission of torque, ,sid uid pressure means including a plurality ofdyn'amically and .statically balanced circumferentially arran-gednand radially outwardly directed rise. and fallca-m surfaces on Vsaid Vone element, means integral with's-aidcasing defining a pluralitydof circumferentially aligned and radiallydn- 'wardlydirected pressure chambers Iarranged relative to theaxis ofi the casing for static -and'dynamic 'balance and facingrsaidV camsurfacesand adapted to contain fluid, said pressure chambers numbering ,twice the raised cam surfaces and comprising two sets, one set being alternate Vones 4of said pressure Vchambers"and the other; set-being the other alternateones ofsaid press chambers, 'pisto'ns y-in said pressure chambers operatively l`engaging? said earn surfaces for reciprocation in response torotationofrfsaid one elementr rel-ativefto said casing, passage means providing fluid'''co-rnin'unicationv betweenfs-'aid-'two sets` of pressure chambers, and" flow i" control 'meansv in said passage means for controlling the rate of iiuid flow between said sets of pressure chambers and thereby for controlling the permitted rate of reciprocation of said pistons, and the other of said rotatable elements and said casing having similar fluid pressure means operatively connecting them for transmission of torque.

9. A transmission comprising a rotatable casing for transmitting an input torque, said casing having an inner portion through which extend two parallel groups `of radially arranged pressure chambers and an outer portion enclosing the inner portion and the radially outer ends of said pressure chambers, a pair of rotatable elements coaxially aligned in said casing, each of said elements having 'a plurality of circumferentially arranged and radially outwardly direc-ted rise and fall cam surfaces, the cam surfaces of one of said elements facing the pressure cham-bers of one of said groups and the cam surfaces of the other element facing the pressure chambers of the other group, pistons in Isaid two groups of pressure chambers operatively engaging the cam surfaces that are faced by their respective groups of pre-ssure chambers for reciprocation in response to rotation of their associated elements relative to said casing, said inner and outer portions dening between them rst, second and third circumferential ducts the first of which is in communication with certain of the pressure chambers of both groups and the second and third of which are in communication only with the other of the pressure chambers of the one group and the other group respectively, `and separate flow control means between said iirst duct and each of said second and third duct-s and operable for controlling the rate of ow of uid reciprocating between said certain pressure chambers and said other @pressure chambers in each group.

it). A transmission as claimed in claim 9 wherein said Y separate flow control means are removably mounted to permit insertion of flow control means of selected capacity.

11. A transmission as claimed in claim 9 including pump means in communication with said first circumferential duct for pumping fluid thereto for repien-ishing uid losses from said pressure chambers or said ducts.

12. A differential transmission comprising a rotatable casing for transmitting an input torque, a set of rotatable differential elements mounted in said casing, one of the rotatable elements of said set having a plurality of circumferentially arranged and radially outwardly directed rise and fall cam surface, said casing having means delining a plurality of circumferentially arranged and radially inwardly directed pressure chambers facing said cam surfaces yand adapted to contain fluid, said chambers having elliptical cross sections with one of their elliptical axes parallel to the axis of said casing, said pressure chambers being in two sets, passage means providing fluid communication between the two sets of pressure chamers, pistons of elliptical cross sections in said pressure chambers and supporting roller cam followers operatively engaging said cam surfaces for reciprocation of said pistons in response to rotation of said one element relative to said casing, said followers having their axes parallel to the axis of said casing, said pressure chambers and said cam surfaces being .arranged so that when relativ-e rotation occurs between said casing `and said one element the pistons reciprocate to transfer the uid in the chambers baci: and forth therebetween via said passage means.

E3. A transmission comprising a rotatable casing for transmitting an input torque, a pair of elements mounted in said casing for independent rotation relative to one another for receiving portions of the input torque, a pair of axle shafts operatively connected `for differential action to lsaid rotatable elements, a torque transmitting mechanism operatively disposed between said casing and each of said elements for .transmitting portions of said input torque from said casing to each of said elements, said torque transmitting mechanism allowing limited rotation of said cas-ing relative to both of said elements simultaneously at low rates of turning of said casing relative to said elements being responsive to progressively increasing rates of turning of said casing relative to each element to progressively increase the torque transmission to such element.

References Cited bythe Examiner UNITED STATES PATENTS 1,420,798 6/22 Weston 74--650 1,429,100 9/22 Ross 74-650 2,978,929 4/61 Roberts 74-711 FOREIGN PATENTS 535,077 3/41 Great Britain.

DON A. WAITE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,198,035 August 3, 1965 Otto Mueller It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l0, line 32, after "elements" insert and Signed and Sealed this 15th day of February 1966n (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD I. BRENNER Commissioner of Patents 

1. A TRANSMISSION COMPRISING A ROTATABLE CASING FOR TRANSMITTING AN INPUT TORQUE, A PAIR OF COAXIALLY ALIGNED ROTATABLE ELEMENTS MOUNTED IN SAID CASING AND ADAPTED TO BE CONNECTED RESPECTIVELY TO A PAIR OF SHAFTS, EACH OF SAID ELEMENTS HAVINGA PLURALITY OF CIRCUMFERENTIALLY ARRANGED AND RADIALLY OUTWARDLY DIRECTED RISE AND FALL CAM SURFACES, SAID CASING HAVING MEANS DEFINING IN AXIALLY SPACED RELATION TWO GROUPS OF CIRCUMFERENTIALLY ALIGNED AND A RADIALLY INWARDLY DIRECTED PRESSURE CHAMBERS, ONE OF SAID GROUPS FACING THE CAM SURFACES OF ONE OF SAID ELEMENTS AND THE OTHER OF SAID GROUPS FACING THE CAM SURFACES OF THE OTHER OF SAID ELEMENTS, THE PRESSURE CHAMBERS OF SAID TWO GROUPS EACH BEING IN TWO SETS, RESTRICTIVE PASSAGE MEANS ASSOCIATED WITH EACH GROUP PROVIDING FLUID COMMUNICATION IN EACH GROUP BETWEEN THE TWO SETS OF PRESSURE CHAMBERS THEREOF, PISTONS IN SAID TWO GROUPS OF PRESSURE CHAMBERS OPERATIVELY ENGAGING THE CAM SURFACES THAT ARE FACES BY THEIR RESPECTIVE GROUPS OF PRESSURE CHAMBERS FOR RECIPROCATION IN RESPONSE TO ROTATION OF THEIR ASSOCIATED ELEMENTS RELATIVE TO SAID CASING, SAID TWO GROUPS OF PRESSURE CHAMBERS AND THEIR ASSOCIATED CAM SURFACES BEING ARRANGED SO THAT WHEN RELATIVE ROTATION OCCURS BETWEEN SAID CASING AND EITHER OF SAID ELEMENTS THE PISTONS ASSOCIATED WITH THE CAM SURFACES OF SUCH ELEMENT RECIPROCATE TO TRANSFER THE FLUID IN THE ASSOCIATED GROUP OF PRESSURE CHAMBERS BACK AND FORTH BETWEEN ITS TWO SETS VIA THE ASSOCIATED PASSAGE MEANS. 